Various methods have been employed for extracting lipids from biomass. Techniques include direct extraction of the biomass with solvents, heating, pressure waves generated via electric arcs, direct saponification via KOH and ethanol, sonication, freezing and grinding and bead mills. For example, the biomass can be dried and the lipid extracted with a solvent such as hexane. Alternatively, a microbial fermentation broth can be subjected to extreme conditions of pH and/or temperature or additional equipment such as a homogenizer can be used to disrupt the cells.
Problems with prior methods include poor product quality due to chemically aggressive conditions of high temperature and high pH, high costs due to the need to dry the biomass or for additional equipment such as homogenizers and pressure vessels.
The “fishy” and “painty” flavors associated with many polyunsaturated fatty acids (PUFAs) found in lipids are primarily due to oxidation of the double bonds in the fatty acids. These flavor and odor notes are normally considered defects that can preclude their use in foods or other applications. The oxidative state and stability of a lipid or lipid-containing material can be measured in a number of ways. Standard measurement techniques include “anisidine value,” “peroxide value,” “oxidative stability index,” “Rancimat,” and gas chromatograph headspace analysis for oxidation products. Information on these different techniques is available from the AOCS (American Oil Chemists' Society) as well as from other sources.
The oxidative state of the lipid or lipid-containing material is strongly impacted by the processing conditions used to make the material. For food materials, the conditions during processing as well as the actual ingredients and quality of the ingredients will affect the oxidation state. For fermentation-derived lipids (e.g., lipids obtained from microbes grown in fermentors, ponds, etc.), the ingredients (fermentation and post-fermentation) used as well as the conditions during the lipid extraction and fermentation will affect the quality. Other sources of PUFAs, such as agricultural crops and animal sources, will also be affected by the processing conditions used to obtain the lipids and lipid-containing materials.